Tactile sensor using elastomeric imaging

ABSTRACT

A tactile sensor includes a photosensing structure, a volume of elastomer capable of transmitting an image, and a reflective skin covering the volume of elastomer. The reflective skin is illuminated through the volume of elastomer by one or more light sources, and has particles that reflect light incident on the reflective skin from within the volume of elastomer. The reflective skin is geometrically altered in response to pressure applied by an entity touching the reflective skin, the geometrical alteration causing localized changes in the surface normal of the skin and associated localized changes in the amount of light reflected from the reflective skin in the direction of the photosensing structure. The photosensing structure receives a portion of the reflected light in the form of an image, the image indicating one or more features of the entity producing the pressure.

PRIORITY INFORMATION

More than one reissue patent application has been filed for the reissueof U.S. Pat. No. 8,411,140, which include U.S. Reissue patentapplication Ser. No. 13/971,456, filed Aug. 20, 2013, U.S. Reissuepatent application Ser. No. 14/045,668, filed Oct. 3, 2013, U.S. Reissuepatent application Ser. No. 14/045,647, filed Oct. 3, 2013, U.S. Reissuepatent application Ser. No. 14/045,620 filed Oct. 3, 2013, and U.S.Reissue patent application Ser. No. 14/045,594 filed Oct. 3, 2013. Thisapplication is a continuation reissue of application Ser. No.13/971,456, which is an application for reissue of U.S. Pat. No.8,411,140, and thereby claims priority from provisional application Ser.No. 61/073,904 filed Jun. 19, 2008, which is incorporated herein byreference in its entirety.

SPONSORSHIP INFORMATION

This invention was made with government support under grant numberBCS-0345805 awarded by the National Science Foundation. The governmenthas certain rights in this invention.

BACKGROUND OF THE INVENTION

The invention is related to the field of sensors, and in particular totactile sensors.

A variety of 2-D tactile sensors have been described in the art. In atypical sensor, an array of individual elements change some electricalproperty, such as resistance or capacitance, in response to pressure.The electrical changes are sensed and conveyed via wires or otherelectronic means to the controller or user. Another type of tactilesensor is optical. Some optical properly such as luminance orreflectance changes as a result of pressure, and a light sensing systemdetects and conveys the signal to the controller or user.

For an application such as a robot fingerpad, there are a number ofproperties that are desired in a tactile sensor. It should have highresolution (be able to make fine spatial discriminations), have highsensitivity (be able to detect small variations in pressure), and becompliant (able to elastically deform in response to pressure). Thetactile sensor should be manufacturable with reasonably large areas. Itshould be easily manufactured using inexpensive materials. It has beenimpossible to achieve all of these goals in a single sensor.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a tactilesensor including a photosensing structure, a volume of elastomer that iscapable of transmitting an image, and a reflective skin covering thevolume of elastomer. The reflective skin is illuminated through thevolume of elastomer by one or more light sources, and has particles thatreflect light incident on the reflective skin from within the volume ofelastomer. The reflective skin is geometrically altered in response topressure applied by an entity touching the reflective skin, thegeometrical alteration causing localized changes in the surface normalof the skin and associated localized changes in the amount of lightreflected from the reflective skin in the direction of the photosensingstructure. The photosensing structure is positioned to receive a portionof the reflected light in the form of an image, the image indicating oneor more features of the entity producing the pressure.

According to another aspect of the invention, there is a method ofperforming tactile sensing. The method includes providing a volume ofelastomer capable of transmitting an image, and covering the volume ofelastomer with a reflective skin. The reflective skin is illuminatedthrough the volume of elastomer by one or more light sources, and hasparticles that reflect light incident on the reflective skin from withinthe volume of elastomer. The method also includes geometrically alteringthe reflective skin in response to pressure applied by an entitytouching the reflective skin, the alteration causing localized changesin the surface normal of the skin and associated localized changes inthe amount of light reflected from the reflective skin in the directionof a photo sensing structure. The photosensing structure is positionedto receive a portion of the reflected light in the form an image, theimage indicating one or more features of entity producing the pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the elements of a sensorcomprising a clear elastomer, a reflective skin, a light source, and acamera in accordance with the invention;

FIG. 2 is a photograph illustrating a slab of a clear elastomer coveredwith a skin containing fine gold-colored flakes, pressed against atwenty dollar bill;

FIG. 3 is a photograph illustrating a slab of a clear elastomer coveredwith a skin containing fine gold-colored flakes, pressed against a seaurchin shell;

FIGS. 4A-4D are schematic diagrams illustrating the elements of animaging system that can be used in a compact structure;

FIGS. 5A and 5B are schematic diagrams illustrating the elements of animaging system using diffused light and edge illumination in accordancewith the invention;

FIGS. 6A-6B are schematic diagrams illustrating the technique used inaccordance with the invention to measure deformation and shear;

FIGS. 7A and 7B are schematic diagrams illustrating the various tactilesensor arrangements used in accordance with the invention;

FIG. 8 is a schematic diagram illustrating a structure to reconstruct 3Dshape of an object;

FIG. 9 is a schematic diagram illustrating a large area high resolutionsensor formed by tiling a set of smaller sensors;

FIG. 10 is a schematic diagram illustrating a contact image sensor (CIS)linear array being used directly in a tactile sensor structure inaccordance with the invention;

FIG. 11 is a schematic diagram illustrating a fabric covering on thereflective skin; and

FIG. 12 is a schematic diagram illustrating the use hair or whiskers onthe inventive tactile sensor structure.

FIG. 13 is a schematic diagram illustrating the elements of a rollingscanner.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a new approach to making tactile sensors thatattain high sensitivity, high spatial resolution, and low cost. Inaddition, it can be built in a compliant form, so that a robot fingerincorporating this sensor can deform elastically in depth, following theprofile of the object being manipulated, thereby allowing good control.

An exemplary embodiment of the invention, as shown in FIG. 1, is madefrom slab of clear elastomer, 3, supported by a rigid sheet 7 made ofglass or other rigid clear material. The surface of the elastomer iscoated with a reflective layer 2, referred to as the “skin,” which ismade, for example, from an elastomeric paint comprising metallic powderembedded in an elastomeric material. The skin has an inner surface(facing the elastomer) and an outer surface (facing the outside world).Light from an illuminator 5 passes through the rigid support 7 and theclear elastomer 3 and strikes the reflective skin 2. When an object suchas a finger 1 applies pressure to the outer surface of the skin, itcauses a distortion of the skin. Local variations in pressure lead tolocal variations in the skin's surface normal. A change in the surfacenormal leads to a change in the amount of light reflected in a givendirection. A camera 4 views the inner skin and records the reflectedlight as an image. The image pattern is the result of the pressurepattern, and thus conveys information about the pressure pattern. Notethat the image pixel values do not directly encode pressure. They encodethe angle of surface normal, which is indicative of the spatialvariation of the pressure.

The clear elastomer can be composed of a wide range of materialsincluding but not limited to silicone rubber, polyurethane,thermoplastic elastomer, plastisol, natural rubber, polyisoprene,polyvinyl chloride, or a mixture thereof. Typically, the hardness of theelastomer, as measured on the Shore A scale, will range between 5 and90. The reflective skin is also elastomeric, and will typically have ahardness that is equal to or greater than that of the clear elastomerbody. The reflective skin may be comprised of the same material as thebody, or of a different material.

The sensor skin can be made by adding reflective particles to theelastomer when it is in a liquid state, via solvent or heat, or beforecuring. This makes a reflective paint that can be attached to thesurface by standard coating techniques such as spraying or dipping. Theskin may be coated directly on the surface of the bulk elastomer, or itmay be first painted on a smooth medium such as glass and thentransferred to the surface of the bulk material and bound there. Also,the particles (without binder) can be rubbed into the surface of thebulk elastomer, and then bound to the elastomer by heat or with a thincoat of material overlaid on the surface. Also, it may be possible toevaporate, precipitate, sputter, other otherwise attach thin films tothe surface.

The reflective particles in the skin may reflect light directionally ornon-directionally. If the particles reflect light uniformly in alldirections regardless of the light's angle of incidence, the resultingskin will behave like a Lambertian surface, which is entirelynon-directional. Titanium dioxide powder, as is used in white paint,leads to a largely Lambertian reflectance. If the reflective particlesare comprised of fine metal flakes, and if these flakes tend to bealigned with each other, then the skin will reflect light directionally,meaning that, for a given angle of incident light, there will be anon-uniform distribution of reflected light. If the metal flakes areflat and mirror-like, and if they are well aligned with each other, thedistribution of reflected light will be highly directional. If the metalflakes are rough or irregular, or if there is randomness in theiralignment, then the distribution of reflected light will be moderatelydirectional, with an appearance resembling sandblasted metal.Directional reflectance can also be obtained with flakes of othermaterials such as mica. In addition there are pigments comprising flakescovered with multilayer interference coatings that can have differentdirectionality for different wavelengths of light.

Further still, metal flake powder of aluminum can be used.

Skin with highly directional reflectance illuminated by a highlydirectional light source yields a device that is sensitive to smallvariations in pressure. This sensitivity can be increased by recordingthe skin's image in its resting state, and using this as a baselineimage that is subtracted from images recorded when pressure is appliedto the skin. Softer elastomers lead to devices that are more sensitiveto low amplitude pressure patterns.

FIG. 2 shows an image obtained with a skin containing gold-coloredbronze flakes that are directionally selective. A slab of a clearelastomer about 1 cm thick, was mounted on a sheet of glass. The slabwas coated with a thin skin containing fine gold-colored flakes. Theslab was pressed against a twenty dollar bill, and the skin was viewedthrough the glass and the elastomer. Due to the way that bills areprinted, the printing on a twenty dollar bill has a raised relief. Whenthe skin is pressed against the bill, its surface deforms in accordancewith the bill's relief. The deformation causes a variation in the amountof light reflected toward the camera, revealing the fine details of thebill's surface in the form of an image.

Another example is shown in FIG. 3. A slab of clear elastomer was coatedwith a reflective skin made with bronze flakes and was placed, skin sideup, on the platen of a flatbed scanner. A sea urchin shell was pressedagainst the reflective skin, causing 3D deformation in the contactregion 6. The untouched region 8 remained smooth and the image of thisregion retained its original smooth appearance. The scanner's internallight source was reflected differently depending on the reflectiveskin's surface normal, resulting in an image that is recognizable as ashaded relief of the sea urchin shell.

The image pixel values do not directly encode pressure. If spatiallyuniform pressure is applied to the entire skin surface, there will be nochange in surface normal and thus no observable variation in the image.The image pixel values depend on surface normal, which in turn dependson the spatial derivative of pressure. Thus, it is the pattern ofpressure variation across the surface that is encoded in the image.

Pressure can be applied to the skin by a rigid object or a non-rigidobject. In the case of a non-rigid object, such as a fingertip, both theobject and the skin will deform, and the skin's shape will depend on thebalance of pressures that the skin and the object exert on each other.Pressure can also be applied by a liquid or gas. For example, a streamof water striking the skin causes it to deform, and the pattern ofdeformation is visible in the image. If the skin and the elastomer aremade of very soft gel-like materials, and if at froth of soap bubbles isplaced in contact with the skin, one can visualize the forces exerted bythe soap bubble walls.

FIGS. 4A-4D show the elements of the imaging system that can be used ina compact structure such as a robot fingertip. In the illustratedembodiment, there is a rounded piece of elastomer, which is mounted on arigid member.

FIG. 4A shows a pair of LEDs 12 and a small camera 14, which are lookingthrough the rounded piece of elastomer 16 positioned on a rigid support17. The skin 18 of the elastomer is reflective, and the camera forms animage of the inner side of the skin. FIG. 4B shows an example whereinthe camera is a pinhole camera 20. FIG. 4C shows a folded path opticalsystem that utilizes a curved mirror 22 which reflects light from theskin to the camera 24. FIG. 4D shows the case Where the skin is imagedwith an endoscope 26 (or the related videoscope, borescope, fiberscope,or the like). This allows the camera 28 to be placed at a distance fromthe sensor.

FIG. 5A shows an exemplary embodiment of a sensor 30 using an extendeddiffuse source of light 31. The diffuse light source 31 and camera 36are positioned on a rigid support 32. A volume of clear elastomer 34 ispositioned on the rigid support 32.

To make the structure compact, it may be preferable to introduce thelight at the edge of the support. FIG. 5B shows another exemplaryembodiment of the invention where one or more light sources 33illuminates the sensor from a side or edge of the support 32, preferablymade of glass or other clear material. Light will bounce off the backface of the support by total internal reflection, and will also bereflected by the reflective skin surface 38 by ordinary reflection. Thiswill cause many of the light rays to remain within the glass+elastomervolume; these rays will illuminate the reflective skin surface 38, andthe surface can be viewed by the camera 36. It may be advantageous touse a glass wedge rather than an ordinary sheet of glass. With a wedge(for example, the “Light Wedge” book light) the light reflects oft thefront and back faces successively, making a larger angle with eachbounce. This causes a greater amount of light to exit the wedge atlarger distance from the light source.

FIGS. 6A-6B show two exemplary embodiments of the invention whereindeformation and shear can be sensed. Deformation (in particular, changesin surface normal) can be sensed by measuring the change in intensity ateach point on the skin 44 produced by a work piece 46, as shown in FIG.6A. FIG. 6B shows a case in which the surface 48 exerts shear forces onthe elastomer and skin 50, causing no change in surface normal, butcausing a lateral displacement. The skin typically contains a visiblemicrotexture due to the random pattern of reflective particles, andshear causes a displacement of this microtexture. Motion analysismethods can then be used to estimate the shear.

In some applications it is desirable that the light source and thecamera be placed at optical infinity so that the angle of incidence andreflectance are parallel when the device is in its resting state. Thiscauses the devices optical properties to be spatially uniform across therecorded image. FIG. 7A shows a slab of elastomer 136 covered withreflective skin 134 and mounted on lens 146. An object 138 appliespressure to skin 134. The focal length of the lens is such that thelight rays from light source 140 are refracted to be parallel whenstriking skin 134. Camera 144 views the skin through the same lens. Theoptical properties of the skin 134 as observed by camera 144 will befairly uniform across the image.

FIG. 7B shows an arrangement in which a slab of elastomer 160 is coveredby a reflective skin 152. The elastomer is mounted on a right angleprism 162. Light source 156 passes through lens 164, emerging asparallel rays that enter prism 162 and strike skin 152. An object 154presses on the skin 152, causing local variation in surface normal.Camera 158 views the skin through a lens 166 that places the skin atoptical infinity for that camera. The optical properties of the skin asobserved by the camera will be fairly uniform across the image.

In accordance with another exemplary embodiment of the invention, it isdesirable to reconstruct the 3-D shape of the deformed surface. In FIG.8, there are two light sources, 80 and 82, which illuminate the skin 84thought the elastomer 79. Preferably, the two light sources illuminatethe surface from substantially different azimuths, for example onealigned with the x-axis and the other with the y-axis of the slab. Thelight sources are turned on one after the other and two images arerecorded by camera 78. These two images can then be analyzed in accordwith the known methods of photometric stereo to estimate the surfacenormal and surface height at every position. If the two lights 80 and 82are of different colors, for example red and blue, and if the camera 78is a color camera, then it is possible to record the two images at thesame time in separate color charnels. Photometric stereo benefits fromthe use of additional images. With a color camera it is straighforwardto use three light sources and to separate the channels into threeimages. Alternately, one can use an arbitrary number of light sources ifthey are turned on one at a time.

The use of multiple lights to get multiple images is useful even when 3Dreconstruction is not being performed. Each light brings out surfacenormal variation along one axis, but not along the orthogonal axis. Byusing two or more lights, the lights can be arranged so that one lightreveals the relief that is missed by another light. This makes itpossible to distinguish a wide range of surface normals in differentdirections. The preferred method of using two or more lights is to havethem be different colors, so that a color camera will separate theinformation about the different lights into different color channels.

It is also possible to use standard stereoscopic techniques as well, inwhich multiple cameras are placed in different azimuths relative to theskin of the sensor. The techniques set forth herein of sensing changesin luminance are believed to yield better sensitivity and resolution inmany applications relative to known techniques. Furthermore, stereopsiscan be used in combination with the techniques disclosed herein. Themicrotexture of the skin and/or the deformation image can be used toestablish correspondence.

In some applications it is desirable to make a sensor surface thatcovers a large area. For example one may require a touchpad that coversan entire desktop. If the device is simply scaled up, then the cameramust be placed at a large distance from the surface, making the deviceundesirably large. One way to ameliorate this problem is to use themethods of folded optics that are used, for example, in many rearprojection televisions. Another way is to use a tiled array of cameras,as shown in FIG. 9. The reflective skin 180 covers the clear elastomer182 which is mounted on a rigid transparent support 184. An array ofcameras 186 is placed a short distance from the elastomer and skin. Thecameras can be arranged so that their image slightly overlap, and theseimages can be combined into a single large image by standard stitchingtechniques.

In another embodiment, a sensor is formed into a cylinder, which can berolled over the surface of the object. In one illustrativeconfiguration, the sensor would look like a brayer or paint roller. Asthe roller rolls over the surface, a video camera inside the roller isaimed continuously at the portion that is in contact with the surface ofthe object. The series of images so obtained can be combined into asingle image by the same methods that are used to obtain panoramicphotographs from a series of smaller photographs.

Alternatively, the roller could be in a fixed position while the surfaceof interest was pulled over it. For example, as shown in FIG. 13, anillustrative embodiment of a rolling scanner is a counterfeit banknotedetector 300 which has a clear elastomer 310 formed into a cylinder, anda reflective skin 320. The detector 300 also has a slot 330 for feedinga banknote 340. A roller 350, driven by a motor, pulls in the banknote340 and forms an image of the banknote's surface shape based on anembossed surface of the banknote's paper and/or the raised level ofprinted ink. A genuine banknote will have a known profile, and amismatch would indicate a counterfeit banknote.

In some applications it is advantageous for the skin to have a texturerather than being smooth. In some situations one wishes to study thedistribution of pressures across a region of human skin. For example,when a skin care product is applied to the skin, the application processproduces a certain distribution of pressure on the skin which changesover time. In order to estimate this changing distribution, a sensor canbe made that mimics the texture, elasticity, and other properties ofhuman skin. When a skin care product is, for example, wiped across theartificial skin, it causes the skin to distort in a manner similar tothat of human skin. The pattern of distortion can be assessed by makinga tactile sensor with mechanical properties emulating human skin. Thismeans that the reflective skin has texture and elasticity like the upperlayer of human skin, and the clear elastomer beneath the skin hasmechanical properties like the deeper layers of human skin. Multiplelayers of clear elastomer with different mechanical properties arerequired to mimic the complex properties of human skin. When a skin careproduct is applied to this device, the reflective skin distorts inresponse to the mechanical forces applied to it, and this distortion isviewed by a camera looking through the clear elastomer layers.

In some applications it may be desired to study the distribution ofpressure over the surface of a specific object, such as a tire or thesole of a shoe. It is possible to form the tactile sensor into the sameshape as this specific object, and with the same hardness or othermechanical properties as this specific object.

In other embodiments, it is not necessary that the image be formed by acamera. Many flatbed scanners use a Contact Image Sensor, or CIS, whichis a linear array of lenses and photosensors placed in close contactwith the object being scanned. No image forming lens is required. FIG.10 shows a strip of elastomer 198 covered with reflective skin 192 andmounted on CIS 194. When object 196 presses on the skin, it modifies thesurface normal, which modifies the amount of light that will bereflected toward the photosensing elements in that neighborhood. Theresult is a 1D image that encodes information about the location andamplitude of the pressure variation on the skin.

In another embodiment, a multitouch touchscreen device is made inconjunction with a flat panel LED display. A thin sheet of clearelastomer, covered with a semi-reflective skin, covers the front surfaceof the display. Most of the light that is emitted by the LED's passesthrough the skin and is seen by a viewer. A portion of the light isreflected by the skin back toward the LEDs. LEDs have the ability to actas photosensors, and thus can be used to measure the amount of reflectedlight. Pressure variation on the skin causes local changes in thesurface normal, which changes the amount of light reflected toward anygiven LED in the array. The LED photosensing responses comprise an imagethat is indicative of the pattern of pressure on the skin. This imageindicates where the user is touching the screen. In addition, becausethis is an inherently high resolution image, it is possible to detectthe fingerprint of the user. This allows each finger of each user to bedistinguished.

FIG. 11 shows another exemplary embodiment of a tactile sensor 202 inaccordance with the invention. A stretchy fabric is placed over thereflective skin. For some applications such a robot manipulator thisfabric will produce a surface with desirable mechanical qualities,including the frictional qualities and the ability to withstand theforces of industrial usage. FIG. 11 shows a cross section of a fabriccovering 204 that is attached to the reflective skin 206 on the clearelastomer 208. An object 214 presses on the fabric causing the skin totake on the texture 210 of the fabric. In the case of a woven fabricthis pattern appears as a gridwork of fibers corresponding to thefabric's construction. Greater pressure leads to a higher contrastfabric pattern, as seen by camera 212. Local properties of this pattern,including the mean value and the contrast, are indicative of thepressure applied at that location.

In another exemplary embodiment, the device is used to measure fluidflow. FIG. 12 shows hairs or whiskers 220 that are attached to thereflective skin 224 at attachment points 222. The attachment points aresmall pads that are rigidly attached to the whiskers. When fluid flowsacross the whiskers, it causes the whiskers to tilt, causing theattachment pads to tilt, causing the reflective skin's surface normal tochange. The skin is viewed by a camera, and the variation in surfacenormal causes a variation in image radiance from point to point. Theimage indicates the speed and direction of fluid flow across eachwhisker.

There are applications for which high resolution is not needed and notdesirable. An extra layer of elastomer on top of the skin acts as amechanical lowpass filter. For example, a 1 mm thick layer reduces theresolution to be on the order of 1 mm.

A fluorescent pigment can be used in the skin, illuminated byUltraviolet (UV) light or blacklight. If the blacklight comes at agrazing angle, it can readily reveal variations in surface normal. Thematerial will be fairly close to Lambertian. To reduce interreflections,one would select a surface that appears dark to emitted wavelengths.This principle is true with ordinary light as well. If one is using aLambertian pigment in the skin, it is better for it to be gray thanwhite, to reduce interreflections.

Blacklight or UV can be used to illuminate a fluorescent surface, whichwould then serve as a diffuse source. In some cases, it would be usefulto use a single short flash (for instance, recording the instantaneousdeformation of an object against the surface) or multiple periodic(strobed) flashes (to capture rapid periodic events or to modulate onefrequency down to another frequency.)

Although the present invention has been shown and described with respectto several preferred embodiments thereof, various changes, omissions andadditions to the form and detail thereof, may be made therein, withoutdeparting front the spirit and scope of the invention.

What is claimed is:
 1. A tactile sensor comprising: a photosensingstructure; a volume of elastomer capable of transmitting an image; and areflective skin covering said volume of elastomer, said reflective skinbeing illuminated through said volume of elastomer by one or more lightsources, said reflective skin having particles that non-directionallyreflect light incident on the reflective skin from within the volume ofelastomer, said reflective skin being geometrically altered in responseto pressure applied by an entity touching said reflective skin, saidgeometrical alteration causing localized changes in the surface normalof said skin and associated localized changes in the amount of lightreflected from said reflective skin in the direction of saidphotosensing structure; wherein said photosensing structure ispositioned to receive a portion of said reflected light in the form ofan image, said image indicating one or more features of the entityproducing said pressure.
 2. The tactile sensor of claim 1, wherein saidvolume of elastomer comprises silicone rubber, polyurethane, plastisol,thermoplastic elastomer, natural rubber, polyisoprene, polyvinylchloride or a mixture thereof.
 3. The tactile sensor of claim 1, whereinsaid volume of elastomer comprises a Shore A hardness between 5 and 90.4. The tactile sensor of claim 1, wherein the volume of elastomer is inthe form of a slab.
 5. The tactile sensor of claim 1, wherein saidphotosensing structure comprises a camera.
 6. The tactile sensor ofclaim 1, wherein said photosensing structure comprises an array ofsensing elements.
 7. The tactile sensor of claim 1, wherein said one ormore features comprise roughness of said entity.
 8. The tactile sensorof claim 1, wherein said one or more features comprise the location,amplitude, or direction of the applied pressure.
 9. The tactile sensorof claim 1, wherein said one or more features comprise the shape, size,or profile of an object producing said pressure.
 10. The tactile sensorof claim 1, wherein said one or more features comprise the motion orslip of a surface touching the reflective skin.
 11. The tactile sensorof claim 1, wherein the sensor has physical properties that are similarto those of human skin.
 12. The tactile sensor of claim 1, wherein thesensor is formed in the shape of a specified object.
 13. The tactilesensor of claim 1, wherein the reflective skin is illuminated by two ormore light sources of different colors.
 14. A method of performingtactile sensing, comprising: (a) providing a volume of elastomer capableof transmitting an image; (b) covering the elastomer with a reflectiveskin having an inner surface facing the elastomer and an outer surface,wherein the reflective skin comprises particles that non-directionallyreflect light incident on the inner surface from within the volume ofelastomer; (c) illuminating the reflective skin through the volume ofelastomer with one or more light sources, wherein at least a portion ofthe light is reflected by the inner surface of the reflective skin; (d)contacting the outer surface of the reflective skin with an entity,wherein the contact produces pressure that geometrically alters thereflective skin, wherein the alteration causes localized changes in theinner surface of the reflective skin, and wherein the localized changesin the inner surface of the reflective skin cause associated localizedchanges in the light reflected from the inner surface of the reflectiveskin; (e) positioning a photosensing structure to receive a portion ofthe light reflected from the inner surface of the reflective skin in theform of an image indicating one or more features of the entitycontacting the outer surface of the reflective skin.
 15. The method ofclaim 14, wherein said volume of elastomer comprises silicone rubber,polyurethane, plastisol, thermoplastic elastomer, natural rubber,polyisoprene, polyvinyl chloride or a mixture thereof.
 16. The methodoff claim 14, wherein said volume of elastomer comprises a Shore Ahardness between 5 and
 90. 17. The method of claim 14, wherein thevolume of elastomer is in the form of a slab.
 18. The method of claim14, wherein said photosensing structure comprises a camera.
 19. Themethod of claim 14, wherein said photosensing structure comprises anarray of sensing elements.
 20. The method of claim 14, wherein said oneor more features comprise roughness of said entity.
 21. The method ofclaim 14, wherein said one or more features comprise the location,amplitude, or direction of the applied pressure.
 22. The method of claim14, wherein said one or more features comprise the shape, size, orprofile of an object producing said pressure.
 23. The method of claim14, wherein said one or more features comprise the motion or slip of asurface touching the reflective skin.
 24. The method of claim 14,wherein the sensor has physical properties that are similar to those ofhuman skin.
 25. The method of claim 14, wherein the sensor is formed inthe shape of a specified object.
 26. The method of claim 14, wherein thereflective skin is illuminated by two or more light sources of differentcolors.
 27. A tactile sensor comprising: a photosensing structure; and avolume of elastomer capable of transmitting an image, the volume ofelastomer having a reflective surface, the reflective surface havingparticles that cause the reflective surface to reflect light incident onthe reflective surface from within the volume of elastomer with adirectional selectivity ranging from moderately directional tonon-directional, the reflective surface being geometrically altered inresponse to pressure applied by an entity touching the reflectivesurface, the geometrical alteration causing localized changes in thesurface normal of the surface and associated localized changes in theamount of light reflected from the reflective surface in the directionof the photosensing structure; wherein the photosensing structure ispositioned to receive a portion of the reflected light in the form of animage, the image indicating one or more features of the entity producingthe pressure.
 28. The tactile sensor of claim 27, wherein the reflectivesurface comprises the particles bound to the elastomer.
 29. The tactilesensor of claim 27, wherein the reflective surface comprises theparticles included in a paint, the paint being applied to the elastomer.30. The tactile sensor of claim 27, wherein the reflective surfacecomprises a reflective skin in contact with the elastomer.
 31. Thetactile sensor of claim 30, wherein the reflective skin is bound to theelastomer.
 32. The tactile sensor of claim 27, the particles reflectinglight substantially uniformly in all directions, and the particlescausing the reflective surface to reflect light substantiallynon-directionally.
 33. The tactile sensor of claim 27, the particlescomprising flakes that exhibit at least one of surface roughness,irregular shape, and random alignment relative to each other, and theparticles causing the reflective surface to reflect light moderatelydirectionally.
 34. The tactile sensor of claim 33, the flakes comprisingbronze.
 35. The tactile sensor of claim 33, the flakes comprisingaluminum.
 36. The tactile sensor of claim 27, the particles comprisingtitanium dioxide.
 37. A method of performing tactile sensing,comprising: providing a volume of elastomer capable of transmitting animage, the elastomer having a reflective surface having an outersurface, the reflective surface having particles that cause thereflective surface to reflect light incident on the reflective surfacefrom within the volume of elastomer with a directional selectivityranging from moderately directional to non-directional; illuminating thereflective surface through the volume of elastomer with one or morelight sources, wherein at least a portion of the light is reflected bythe reflective surface; contacting the outer surface of the reflectivesurface with an entity, wherein the contact produces pressure thatgeometrically alters the reflective surface, wherein the alterationcauses localized changes in the reflective surface, and wherein thelocalized changes in the reflective surface cause associated localizedchanges in the light reflected from the reflective surface; andpositioning a photosensing structure to receive a portion of the lightreflected from the reflective surface in the form of an image indicatingone or more features of the entity contacting the outer surface of thereflective surface.
 38. The method of claim 37, wherein the reflectivesurface comprises the particles bound to the elastomer.
 39. The methodof claim 37, wherein the reflective surface comprises the particlesincluded in a paint, the paint being applied to the elastomer.
 40. Themethod of claim 37, wherein the reflective surface comprises areflective skin in contact with the elastomer.
 41. The method of claim40, wherein the reflective skin is bound to the elastomer.
 42. Themethod of claim 37, the particles reflecting light substantiallyuniformly in all directions, and the particles causing the reflectivesurface to reflect light substantially non-directionally.
 43. The methodof claim 37, the particles comprising flakes that exhibit at least oneof surface roughness, irregular shape, and random alignment relative toeach other, and the particles causing the reflective surface to reflectlight moderately directionally.
 44. The method of claim 43, the flakescomprising bronze.
 45. The method of claim 43, the flakes comprisingaluminum.
 46. The method of claim 37, the particles comprising titaniumdioxide.